Various methods are known for producing images or duplicates of images. The imaging materials used are, in certain cases, particular organic compounds. Some of these heretofore known methods employ mixtures of inorganic compounds such as silver halide with one or more particular types of organic compounds as sensitizers.
A new photographic process using tellurium compounds to provide the image is disclosed in U.S. patent application Ser. No. 596,646 filed July 17, 1975 (now U.S. Pat. No. 4,142,896). In accordance with U.S. Pat. No. 4,142,896, an emulsion is formed using certain reducible tellurium compounds in combination with a reductant precursor in a binder or matrix suitable for forming a film-like coating on a substrate. The film prepared therefrom is exposed image-wise to activating energy and is thereafter developed as is known in the art hereinafter described. Heat development is preferred.
Some tellurium compounds described for use in the photographic process of U.S. Pat. No. 4,142,896 may be represented, for example, by the formula EQU R.sub.x --Te--X.sub.y ( 1)
in which R is an organic radical containing at least one carbonyl group, X is halogen, preferably chlorine, and x is 1, 2 or 3, and x+y=4. The organic radical R may be either two independent radicals or may be joined together to form a cyclic compound. Another group of compounds mentioned in U.S. Pat. No. 4,142,896 are organic tellurium compounds which may be considered or characterized as tellurium tetrahalide adducts of ethylenic or acetylenic hydrocarbons. Some of such compounds can be represented by the formulae ##STR2## wherein R and R.sup.1 are each the residue of an ethylenic hydrocarbon and X is a halogen, preferably chlorine.
Another category of photosensitive tellurium compounds which have been found useful are halogenated tellurium compounds, such as compounds of the formula EQU TeCl.sub.n Br.sub.m ( 4)
where n is an integer from 2 to 4, and n+m=4. The use of such halogenated tellurium compounds in imaging processes is disclosed in U.S. Pat. No. 4,066,460 to Chang et al.
Still another category of useful tellurium compounds are described in U.S. Pat. No. 4,106,939. These compounds are tellurium tetrahalide adducts of aromatic amines in which nitrogen attached directly or indirectly to the aromatic ring is substituted by alkyls of 1-4 carbon atoms, the adduct being free of diazo groups.
The tellurium compounds such as the foregoing may be employed in conjunction with a reductant-precursor which serves as a sensitizer. The reductant-precursor is a compound which, under the influence of activating energy, will absorb radiation energy and abstract labile hydrogen from an appropriate hydrogen donor to become a strong reducing agent. The strong reducing agent reduces the tellurium compound to a divalent tellurium compound or to elemental tellurium. In either event, a change in optical density occurs which results in an imaging suitable for recording information. In general terms, the foregoing reaction may be represented by the following mechanism: ##STR3## wherein PQ is the reductant precursor sensitizing agent; .sup.1 PQ is the first excited singlet state thereof; .sup.3 PQ is the triplet state thereof; RH is the hydrogen donor; PQ.H.sub.2 is the reductant precursor in its reduced state; and (R.sup.1).sub.2.Te.X.sub.2 is the reducible tellurium image-forming compound.
In this connection, it should be noted that the hydrogen donor need not be specifically provided, although a variety of alcohols can be used if desired. In the absence of a specially-provided hydrogen donor, the labile hydrogen can sometimes be abstracted from the organic resins used as binders. In other cases, the sensitizer can be its own hydrogen donor, and this is known to be the case with at least one sensitizer, namely, isopropoxynaphthoquinone.
A modification of the tellurium photographic process is described in Belgian Patent No. 854,193, wherein certain diols of the formula EQU R.sub.10 --CHOH--Z--CHOH--R.sub.11 ( 5)
may be employed as the hydrogen donor for use in conjunction with the photosensitizer described above. In the foregoing formula, R.sub.10 and R.sub.11 represent hydrogen and various organic substituents. Z may be a direct carbon-carbon linkage between the two hydroxy substituted carbon atoms, or may be any of various linking groups. Reference is made to Belgian Patent No. 854,193 for a fuller description of the diols referred to. In the Belgian patent, these diols are said to serve as hydrogen donors. Subsequent research has suggested that this is not completely accurate. In fact, a major portion of the diol appears to form a complex with the tellurium compound.
This finding has led to the discovery of diols of the general formula EQU R--O--CH.sub.2 CHOH--CH.sub.2 OH (6)
which have improved characteristics when used in tellurium-based photographic films.
The radical R may be a simple aliphatic group (for example, alkyl or alkenyl). Alternatively, the radical R may contain a carbonyl group (for example, an acyl radical). Preferably, however, the radical R is aromatic. Best results are obtained where the aromatic ring is separated from the ether oxygen by one methylene grouping. A more complete description of these diols is contained in U.S. patent application Ser. No. 73,700, filed Sept. 10, 1979, now U.S. Pat. No. 4,281,058, and reference is made thereto for additional descriptions thereof.
Still another modification in the use of tellurium compounds as photosensitive agents involves what is known as a "masked reducing agent". A number of compounds are known, such as phenidone, which will reduce organo-tellurium compounds. The reducing capacity of such compounds may be "masked"--i.e., inhibited--by appropriate substitution. In such cases, if the substituent is one which can be cleaved by the reaction products liberated upon the photoreduction of the tellurium compound, the masked reducing agent can be used to amplify the photoresponse through the mechanism ##EQU1##
Since the organo-tellurium compounds commonly used release hydrogen halides (particularly hydrogen chlorides) as by-products of the reduction reaction, and the reducing agents, such as phenidone, are amino compounds, the masking agents most effectively employed are compounds which will convert the amino nitrogen into an amide. A typical masked reducing agent thus is the compound ##STR4## A more complete description of masked reducing agents may be found in Belgian Patent No. 863,052 of July 19, 1978, and reference thereto is made for additional descriptions thereof.
As an alternative to the masked reducing agents described in Belgian Patent No. 863,052, a new class of masked reducing agents may be substituted, represented by the general formulae ##STR5## wherein Y is hydrogen or ##STR6## said compound containing at least one ##STR7## In the foregoing formulae, R.sup.1 may be alkyl, alkanoyl, alkoxycarbonyl, phenyl, benzyl, benzoyl, nitrophenyl, benzylcarbonyl, phenylmethyl, phenylethyl or phenylpropylcarbonyl, or aminocarbonyl. R.sup.2, R.sup.3 and R.sup.4 each, and independently, may be hydrogen, alkyl or phenyl and amino. R.sup.4 may be phenyl, nitrophenyl, halophenyl, alkyl, mono-, di- or tri-haloalkyl, benzoyl, alkylphenyl, or alkylcyanophenyl. The masking group may be substituted at either one or both of the amino hydrogen sites of the reducing agent. The alkyl groups referred to above may contain up to seven carbon atoms. Such compounds are conveniently accessible through reaction of the parent hydrazine or pyrazoline with an isocyanate of the formula EQU R.sup.5 --N.dbd.C.dbd.O (11)
A more complete description of these masked reducing agents is found in U.S. patent application Ser. No. 277,720, filed June 26, 1981 and reference thereto is made for additional descriptions thereof.
In practice, the foregoing ingredients, i.e., a tellurium derivative, a reductant precursor sensitizer, and additional ingredients such as the glycol and masked reducing agent, are combined in a suitable matrix to form an emulsion which may be spread into a film on an appropriate carrier or substrate. A latent image in the film is formed by exposure to imaging energy, for example, a light image.
After formation of the latent image, a visible image is developed by heating the exposed film as described in U.S. Pat. No. 4,142,896.
The speed or light sensitivity of the film is determined by the amount of energy necessary to produce an image. For many applications it is desirable to have an imaging film that is relatively fast, and in addition, has a low optical density relative to the optical density of the image formed by the film. It is also desirable for the film to be sensitive to light in the visible spectrum facilitating use of the film in many practical applications. The organo-tellurium imaging system previously described generally did not possess the characteristics of sensitivity to visible light while at the same time having good speed, such as less than about 30,000 ergs of imaging energy per square centimeter to achieve an optical density of one greater than fog.